The present invention relates to a catalyst-free methods of forming polyurethanes from pentafluorophenyl carbonates, and more specifically to surfactant assisted interfacial polymerization of pentafluorophenyl carbonates to form polyurethanes.
Polyurethanes (PUs) have been used for a wide range of applications including thermoplastics, surface coatings, textile coatings, adhesives, elastomers, foams and dispersions. The properties of PUs are tailored by the reagents used and the method of preparation. Taking into account the currently large PU production volume, an ongoing need exists for more environmentally friendly (i.e., “greener”) PU syntheses.
PUs are typically produced by an addition reaction between a diisocyanate and a bi-functional and/or multi-functional alcohol. The resulting polymer is an alternating segmented copolymer, where the segments are derived from the monomers. The segments can be “soft” or “hard.” Typically, the soft flexible segments are generated from polymeric diols and diisocyanates (e.g., polyethers, polyesters or polycarbonates), and the hard rigid segments are generally formed from short chain and low molecular weight diisocyanates and diols. The polymeric diols can be biocompatible and/or biodegradable while the diisocyanates, obtained from phosgene, raise severe toxicity issues.
Isocyanate-free approaches to polyurethanes include the reaction of six- and seven-membered ring carbonates with nucleophiles such as diamines. High temperatures and long reaction times are required to generate high molecular weights using this method. Moreover, the cyclic carbonates can be unstable in aqueous media. As a result, polyurethane formation in aqueous media has been limited to the use of isocyanate monomers. Molecular weights of polyurethanes formed under aqueous conditions using isocyanate monomers are considerably lower than those obtained in organic solvents.
Another synthetic approach to polyurethanes utilizes activated aromatic dicarbonates, which undergo condensation with nucleophiles such as diamines to form polyurethanes in organic solvent media. The efficiency of the condensation reaction is dependent on the nature of the leaving group and the structure of the dicarbonate.
Interfacial polymerization is one of the most challenging techniques for polycondensation reactions. Two reactive monomers are dissolved separately in immiscible liquids. In this type of polymerization, rapid reaction occurs at the interface between these two solutions. Examples of interfacial polymerization employed for forming polyurethanes include the reaction of acetals, bis-chloroformates and isocyanates. In each case, the interfacial polymerization is hampered by the instability of the starting materials in aqueous media.
Therefore, more efficient methods of preparing polyurethanes were sought, in particular, catalyst-free methods of forming polyurethane nanoparticles and nanogels using isocyanate-free monomers. Methods compatible with introduction of arbitrary functionality into the polyurethanes for emerging medical and thin film applications are particularly desirable.